Beyond Inhibition: A 1H NMR Investigation of the Early Kinetics of RAFT-Mediated Polymerization with the Same Initiating and Leaving Groups

In situ 1H nuclear magnetic resonance (NMR) spectroscopy has been used to directly investigate the processes that occur during the early stages (typically the first few monomer addition steps) of an AIBN-initiated reversible addition−fragmentation chain transfer polymerization of styrene in the presence of the RAFT agent cyanoisopropyl dithiobenzoate at 70 and 84 °C. The change in concentration of important dithiobenzoate species as a function of time has been investigated. It was found that the reaction was extremely selective during the period of consumption of the initial RAFT agent (defined as the initialization period), with almost no production of RAFT-capped chains of degree of polymerization greater than unity until all of the cyanoisopropyl dithiobenzoate was converted to its single monomer adduct. The rate-determining step for this process was found to be the addition (propagation) of the cyanoisopropyl radicals to styrene. During the period where the initial RAFT agent was consumed, fragmentati...